A magnetic disk drive storage device typically comprises one or more thin film magnetic disks, each having at least one data recording surface including a plurality of concentric tracks of magnetically stored data, a spindle motor and spindle motor controller for supporting and rotating the disk(s) at a selected RPM, at least one read/write transducer or “head” per recording surface formed on a slider for reading information from and writing information to the recording surface, a data channel for processing the data read/written, a positionable actuator assembly for supporting the transducer in close proximity to a desired data track, and a servo system for controlling movement of the actuator assembly to position the transducer(s) over the desired track(s).
Each slider is attached on one surface to an actuator arm via a flexible suspension and includes on an opposite side an air bearing surface (ABS) of a desired configuration to provide favorable fly height characteristics. As the disk rotates, an air flow enters the slider's leading edge and flows in the direction of its trailing edge. The air flow generates a positive pressure on the ABS, lifting the slider above the recording surface. The slider is maintained at a nominal fly height over the recording surface by a cushion of air.
As recording density and data transfer rate have increased over the past a few years, critical dimensions in the recording device such as track width read and write gap and coil size have decreased accordingly. Also, the fly height between the air bearing surface (ABS) and the media has become smaller and smaller. For reference, recording heads with 40 GB/in2 products typically have fly heights of about 12 nanometers. Modern heads have even lower fly heights, and fly heights are expected to continue to decrease. This reduction in head critical dimensions and fly height, while beneficial to magnetic performance, also comes with cost on thermal and mechanic reliability. Particularly, with lower fly heights between the head and the magnetic disk during operation of the disk drive, there is an increasing rate of intermittent contacts between the head and the disk resulting in damage to the disk surface and wear on the head elements.
An important issue that arises in designing a hard disk drive relates to head parking which involves placing a head stack assembly in an appropriate position while there is no power applied to the drive. Generally, some type of head parking is needed to avoid problems that result if a spinup operation is initiated while a head contacts any part of a disk surface that defines a data recording zone. In accordance with some designs, each recording surface has a landing zone at which the head for that recording surface is parked. In accordance with other designs, a ramp loading system is provided. According to this design, a ramp is provided for each slider/suspension assembly at the inner or outer diameter of the disk where the slider is “parked” while the spindle motor is powered down. During normal operation, the disk speed is allowed to reach a selected RPM (which may be below the normal operating RPM) before the head is “loaded” onto the disk from the ramp on the air cushion generated by the disk's rotation. In this manner, the slider flies over the disk without significant contact with the disk surface, eliminating contact start/stop wear. The load/unload ramp structure is generally made of plastic which can be injection molded into complex ramp structures.
The teachings of the prior art regarding ramp loading systems leave unresolved various significant technical difficulties with respect to designing a practical system for a high capacity, high performance, high rpm disk drive. In such a drive employing multiple disks in a disk stack, a tight three-way merge tolerance is demanded not only between the disk stack and the head stack, but also between the head stack and the ramp stack, as well as the ramp stack and the disk stack. The z-height variance of a ramp stack itself has to be minimized, while all the ramps have to be precisely machined to a sophisticated ramp profile, made from a thermally stable and wear resistant materials. The disk flutter at the outer diameter is a function of spin rate; thus, higher rpm drives have greater such disk flutter; this further stresses a tight head/disk merge for any outer diameter load/unload system. This, coupled with dramatically increasing linear velocity at the outer diameter, poses severe risk for loading/unloading a head onto a disk. Thus, the load/unload parameters must be designed to assure no damage for the life of the drive, which is very difficult and often unreliable at high disk velocities used in server and desktop class drives.
In addition, because the head is loaded to a random angular position on the disk, a guard band on the disk surface at the inner or outer diameter has to be allocated to loading/unloading so that potential damage does not cause data loss. However, this represents a significant loss to the premium real estate for data recording, on the order of 5-15% of the full writeable area of the disk.
What is therefore needed is a reliable way to obtain more disk capacity by reducing the area of the disk normally not used for data storage because of potential load/unload damage.